Acoustic testing is a technique which uses sound waves to test an object. Ultrasonic non-destructive testing is one such technique, which has found application in the testing of laminate materials, such as metal laminate systems used in the aerospace industry. Conventional non-destructive testing methods for laminates are based on transmission measurements or very low frequency reflection measurements. These techniques lack the capability of providing information about the depth of defects in the material. In conventional reflection techniques a single transmitter/receiver transducer is arranged to project an acoustic test signal which is incident on the test material at approximately zero degrees (it should be noted that incidence angles are measured with respect to a normal which is at 90 degrees to the surface of the test material). The waves reflected by the test material are then received by the same single transducer. Although some reflection techniques provide some information about the depth of defects, it has been found that, due to the fine layering of laminate materials, the detected reflection images are often very complicated and difficult to process due to the vast number of reflections. Thus, reflection testing techniques have not been considered as a viable option for testing laminate materials.
It is an object of the present invention to address those problems encountered in conventional acoustic testing apparatuses for testing laminate materials. In particular, it is an object to provide a testing apparatus and method which identifies the depth of defects detected in the laminate without requiring complex signal processing.